The present invention relates to a crystal type film thickness meter; and more particularly, the invention relates to a film thickness meter capable of measuring an accurate film thickness, even if a film is peeled.
When a film is formed on a processing object (such as, glass, wafer, etc.) in a vacuum by an evaporation method or the like, a crystal type film thickness meter is used in order to control the film thickness of the thin film during its growth period.
In order to obtain a desired film thickness of the thin film, the film thickness value of the thin film during the film formation is monitored by the crystal type film thickness meter; and the process with a constant film thickness is made possible by terminating the process when the film thickness reaches an aimed film thickness which has been preliminarily set.
Since the film thickness of the thin film formed on the processing object by such a method depends on a numerical value indicated as a film thickness value by the film thickness meter, it is important that the thickness of the film is accurately measured by the film thickness meter in order to stabilize product quality.
From films repeatedly deposited on a crystal oscillator, sometimes exfoliations can occur. If the thin film attached to the surface of the crystal oscillator exfoliates, the film thickness of the exfoliated portion can be removed from the film thickness before the exfoliation. However, the thin film of the processing object is not exfoliated; and thus, the film thickness of the formed film becomes greater than the aimed film thickness if the vapor deposition is terminated when the measured value of the film thickness meter has reached the aimed film thickness, which can result in defective products produced depending upon the thickened degrees.
Since a serious influence can be made particularly in a process during which a thin film having very thin thickness is formed, a measuring technique for avoiding such a problem has been desired.
See, Japan Patent Document JP-A 11-222670.